A drug developed to treat cancer worked as a form of male contraception in mice in a study that may point the way toward a birth control pill for men, researchers said. Scientists found that giving the compound, called JQ1, to mice reduced the number and quality of their sperm, then allowed normal sperm production to resume when the medicine was stopped, according to research described today in the journal Cell. The drug didn’t lower testosterone, interfere with mating or affect health of offspring after JQ1’s use, researchers said.